The invention concerns a control system for automatic adjustment of the rearview mirrors of a vehicle and of the type where the horizontal angular position of the mirror via airborne signals from transmitter and receiver means, is changed by means of a drive unit in response to the mutual horizontal angular position between coupled vehicle parts.
For several years the problems concerning the rearview mirror equipment of trucks have been realized since, as is well known, drivers' rearward vision is insufficient in many traffic situations because the size and height of trucks details that, notwithstanding the improvement in the standard equipment of mirrors (with e.g. near view, rearview and wide angle mirrors), there will always be zones in so-called blind angles which cannot be seen from the cab.
Thus, there are many accidents with trucks, in particular during right-hand turns where, as mentioned, a single rearview mirror cannot provide comprehensive all-embracing vision along the side of the truck precisely because of the blind angles.
Apart from proposals for equipping trucks with more mirrors of different types, attention and efforts have for several years been devoted to various, more or less automatic devices for adjusting rearview mirrors. Thus, e.g. the U.S. Pat. No. 3,469,901 and the U.S. Pat. No. 4,609,265 as well as the EP Patent Application 0 094 817 disclose devices utilizing the relative angular displacement between a front and a rear vehicle part. Thus, they are devices which are essentially just used in connection with combinations of trucks and towed vehicle parts such as trailers or semi-trailers collectively referred to as trailers in the following. Since this system is based on changes in the mutual angular position between the motor vehicle and the trailer, it will be appreciated that the system cannot be used for single vehicles.
In a variety of these systems the angular changes at the so-called fifth wheel of the motor vehicle and the trailer is sensed by a cord drive, one of the front corners of the trailer having secured thereto a cord, a cable or the like whose other end, in a predetermined length, is wound onto a drum which rotates in response to the angular displacement of the motor vehicle with respect to the trailer.
Also so-called steering gear responsive systems for automatic adjustment of rearview mirrors are known. In contrast to the above-mentioned ones' such systems may be used for all types of vehicles, but are vitiated by the serious drawback that the mirror adjust itself in direct response to the angular position of the steered wheels away from straight ahead. Such a device may involve serious consequences, e.g. in the situation where the vehicle parts of a truck and trailer combination are aligned and are perhaps stationary with the steering wheels fully turned to one side, causing the actual field of view to be quite different from the one actually required, and resulting in precisely the undesired blind angles which may cause overlooking of other traffic such as cyclists.
Such a principle is disclosed e.g. in the U.S. Pat. No. 3,640,609. This system however has a relatively complex structure and complicated mode of operation and is consequently rather expensive.
A relatively new development is the so-called wireless detection systems where no mechanical means of transfer are used. The Swedish Published Application 447 087 is an example of this. The principle is that a combined transmitter/receiver device on the motor vehicle of a truck and trailer combination detects reflections against an oppositely disposed object (the trailer) these reflections varying with the angular position of the motor vehicle with respect to the trailer. The signals received are then used for controlling the rearview mirror angle.
This system operates satisfactorily as far as it goes, even during backing and other manoeuvring, but has the drawback that the reflections may be affected by other factors than the angle between the two vehicle parts, e.g. dirt on the reflecting face.
The object of the invention is to provide a control system of the present type which is more reliable than the known ones and which makes it possible to adjust rearview mirrors according to the field of view actually required so as to provide optimum manoeuvrability of the vehicle without any risk of blind angles. Another object of the invention is that the mirror adjusting system is to be of such simplicity as to allow ready mounting on a vehicle without unduly great costs.